Metal containers and in particular steel and aluminium cans, have long been employed for the storage and transport of a wide range of products, including foods and beverages. One reason for the popularity of the can in relation to foods has been its ability to provide a sterile environment for the food product despite what can be significant storage times between filling of the can and ultimate consumption of the product by the consumer.
In the case of foods, heating in a steam pressurised retort is often utilised to cook the food and also ensure that a high enough temperature for a sufficient length of time is achieved to ensure that "commercial sterility" of the contents results. Cans for foods must remain hermetically sealed at temperatures as high as 130.degree. C. retort pressures of more than 40 psi or vacuum pressures of the order of 4-5 inHg. The package should throughout this process and thereafter remain hermetically sealed until the time it is deliberately opened for consumption, and should remain effectively sterilised of pathogenic food spoilage organisms regardless of whether the food is served heated or not. The packaging that has met this requirement has typically been the non-resealable steel can which can withstand the high temperatures during the heat processing cycle and protect the contents against spoilage. Such cans have typically been opened by can openers that remove or puncture one end of the can to allow access to its contents. In more recent times, the use of ring-pull arrangements that allow one entire end of a can to be torn away from the can, and so removing the need for the use of a separate can opener, has also become more widespread.
Steel and aluminium cans have also proved ideal for containing carbonated liquids because of the can's ability to withstand the high internal pressures generated by carbonated liquids, such as soft drinks and beer (eg: pressures of about 96 psi and pasteurisation temperatures of around 60.degree. C. are not uncommon). Such cans have typically had a ring-pull or similar mechanism that can be actuated to form a relatively small orifice in one end of the container. The traditional small orifice has a number of disadvantages, including that it cannot be resealed and that its dimensions slows the rate of consumption of the product in comparison with drinking the beverage from, for example, a glass or similar container. The small orifice also substantially prevents any aromas of the product being detected by the drinker which for many beverages, for example beer, detracts from the enjoyment of drinking the product.
The present invention is directed to an alternative mechanism for sealing the end of a container that retains the advantages of the present techniques whilst overcoming some of their disadvantages.